This is a request for a Scientist Development Award (K21). The proposal of this application is to acquire training and develop expertise on the role of sibling relationships in the development of antisocial behavior. Current research has suggested that siblings may make a substantial and unique contribution to conduct disorder and delinquency. However, questions remain about the precise risk and protective processes by which siblings influence each other. The overall goal is to acquire the requisite skills to conduct definitive studies of how siblings impact on the developmental course of antisocial behavior. Understanding the role siblings play in the etiology of antisocial behavior may inform preventive intervention programs aimed at families at risk, to include siblings as well as parents. This proposal is to acquire additional training necessary for the comprehensive study of sibling influences on antisocial behavior, specifically (1) observational and interview methodology used to examine, in a valid and reliable manner, low frequency and covert antisocial behavior between siblings, and (2) psychiatric epidemiological methods used to design studies employing large, representative community samples, and analytic methods to test hypotheses of the role of sibling relationships on the developmental course of antisocial behavior.